Henry Cavill's training for the role consisted of extensive sword-training (besides the rigorous bodybuilding required to prepare his physique for the camera). He said, "I spent all of my free time, and when I wasn't on set, with a sword in my hand. It was getting used to the weight of the sword, using it day in and day out. I had three swords where I lived, and four at work. And it was just non-stop practice, practice, practice."
Henry Cavill himself actively pursued the role of Geralt until he got it. When Cavill first heard that the show was being made, he repeatedly bothered his agents to get a meeting with Netflix. Finally, Netflix agreed to take the meeting with him but show-runner Lauren Schmidt Hissrich initially turned him down because she hadn't written a single word of the script yet and did not know what the show was going to be. After 4 months, as the show was being written, Schmidt tested 207 actors for Geralt but couldn't find him. She said that while writing the script, she kept hearing Cavill's voice in her head speaking Geralt's lines. Finally, 4 months after their initial meeting, she met Cavill again, and this time during his audition, when he read the lines she had written live in front of her in his real voice, she instantly knew that Cavill was Geralt. Cavill said it was important to go through the process to make sure the right actor was picked and he was thrilled to finally win the role which he called his "dream come true". He went to add "it was an absolute honor to play Geralt because he lives very close to my heart."
Henry Cavill's performance was so on point that he didn't even need much of the dialogue written for this character, writer and show-runner Lauren Schmidt Hissrich revealed, because he was able to convey everything through his performance alone. She said, "In the first episode, I wrote Geralt with a lot of lines. Henry shot them all, and in the edit we started pulling some of them out. Henry brings subtleties to this character, finding emotional resonance in small moments, and playing it in such a subtle way that you understand what the character is going through without necessarily having huge chunks of dialogue. By the time we got to the finale of the first season - we didn't even shoot half the dialogue because we knew there was so much Henry could do with Geralt that didn't require my words."
Vladimir 'Furdo' Furdik, the veteran stuntman and fight designer (of Game of Thrones fame who eventually ended up portraying the Night King on the hit show) praised Henry Cavill's fighting skills as the best he had ever seen in his decades long career. Furdik spoke at length at the Eastern European Comic-Con 2019 about the "dance like" fighting style he created for Cavill's Geralt character, "I think Netflix made a very good decision to give the role to Henry because I don't know anyone else in the world who looks like The Witcher. Or any actor, who has as much experience with the sword as Henry. He's a very good fighter. So it was not difficult for me to teach him anything. He put in a lot of hard work in the fights. Another thing was that we could not copy the (The Witcher) video-game. Video games are completely different. If you are going to kill someone, you can kill them from this side or that side or another side. You can put the sword in, in many ways. I hope you like his style, I tried to give him a more dance-like style. Something that is effortless. He goes through the fight as if he can predict what is going to happen. He knows 3 seconds before killing someone how he will kill him." He also praised Cavill's quick learning skills at Karlovy Vary International Film Festival 2019, "Henry is excellent, without him they (Netflix) wouldn't be able to do (the Witcher show), I can guarantee that. I don't know any actors who are that good with a sword and fight scenes overall as Henry is. I have never met anyone who could learn fight choreography for a scene in two hours." Asked if Cavill was better than Furdik's Game of Thrones co-star Kit Harington, Furdik replied, "Kit didn't have to do such complex moves in his fight scenes (as Henry)."